chapter 12 part 1

Question 1

constitutive (continuous) transcription

Answer 1

occurs for genes needed continuously to perform tasks (housekeeping genes) & are needed for the life of the cell

Question 2

constitutive genes

Answer 2

actively expressed all the time

Question 3

inducible genes

Answer 3

expressed only when their proteins are needed by the cell

Question 4

regulated transcription (inducible)

Answer 4

needed in genes only needed for responses to changing environmental conditions or during certain phases of growth
-induces control of both initiation & amount of transcription

Question 5

what is the major means of regulating gene expression in bacteria?

Answer 5

transcriptional regulation

Question 6

what does transcriptional regulation control?

Answer 6

results from interactions between DNA-binding proteins & regulatory sequences of DNA

Question 7

negative control of transcription

Answer 7

controls binding of a repressor proteins to a regulatory DNA sequence & preventing transcription
-bind to dna sequences called operators through a DNA-binding domain
-binding blocks transcription
-can be turned on or off by binding other components

Question 8

positive control of transcription

Answer 8

involves binding of an activator protein to regulatory DNA & initiating gene transcription
-also have a dna-binding domain
-binding to dna causes rna polymerase to initiate transcription
-turned on or off

Question 9

how many domains to acitvator/repressor proteins (TFs) have & what are they?

Answer 9

at least two
-dna binding domain & allosteric domain

Question 10

what does the dna binding domain do?

Answer 10

it locates & binds operator dna sequence or other target dna sequences

Question 11

what does the allosteric domain bind?

Answer 11

a molecule or protein, which causes a change in conformation of the dna-binding domain, altering its function
-turns dna binding on or off
-this is properly called allostery

Question 12

what are the four categories of gene regulation

Answer 12

negative inducible, negative repressible, positive inducible, positive repressible

Question 13

inducible

Answer 13

the effector molecule causes transcription to START

Question 14

repressible

Answer 14

the effector molecule causes transcription to STOP

Question 15

repressor

Answer 15

negative control

Question 16

activator

Answer 16

positive control

Question 17

all four catrgories of gene regulation require what?

Answer 17

allosteric effector/inducer/inhibitor/co-repressor molecule

Question 18

negative inducible

Answer 18

-TF is a repressor
-binding of the effector molecule to the TF causes transcription to START
-effector molecule is an inducer
-lac operon in ex

Question 19

negative repressible

Answer 19

-TF is a repressor
-binding of the effector molecule to the TF causes transcription to STOP
-effector molecule is a co-repressor
-trp operon is an ex

Question 20

positive inducible

Answer 20

-TF is an activator
-binding of the effector molecule to the TF causes transcription to START (co-activator)
-effector molecule is an inducer

Question 21

positive repressible

Answer 21

-TF is an activator
-binding of the effector molecule to the TF causes transcription to STOP
-effector molecule is an inhibitor

Question 22

what is the most common structural feature of homodimers in bateria?

Answer 22

the helix-turn-helix (HTH) motif, in which two alpha-helical regions interact with the DNA sequences

Question 23

what are the recognition & stabilizing helix separated by?

Answer 23

a turn in each polypeptide

Question 24

operons
-Genes in an operon nearly always participate in the same metabolic or biosynthetic pathway

Answer 24

clusters of genes undergoing coordinated transcriptional regulation by a shared regulatory region

Question 25

where are operons commonly found?

Answer 25

in bacterial genomes

Question 26

can operons be activated or repressed to control activity of a set of genes?

Answer 26

yes! -switching mechanisms are typically responsive to environmental cues

Question 27

what operon of e. coli is responsible for producing three proteins needed for use of lactose

Answer 27

lactose (lac) operon

Question 28

what is the principle energy source for e.coli & most organisms?

Answer 28

glucose -this monosaccharide is metabolized directly by the glycolysis pathway

Question 29

_________ is one of the many sugars that can serve as an alternate carbon source; its utilization is controlled by the lac operon, which is an inducible operon system

Answer 29

lactose -inducible systems are turned on only when an inducer compound (lactose in this case) is available

Question 30

what is lactose made of?

Answer 30

glucose & galactose

Question 31

what bacteria phenotype can grow on media containing lactose as the only sugar?

Answer 31

lac + -they do this by producing a gated channel (permease) at the cell membrane that allows lactose to enter the cell & the enzyme beta-galactosidase to break the beta-galactose linkage

Question 32

what does the breakdown of lactose also produce?

Answer 32

allolactose which acts as an inducer compound

Question 33

what does the lac operon consist of

Answer 33

multipart regulatory region & three structural genes

Question 34

how many binding sites does the regulatory region have?

Answer 34

-promoter (P) that binds to rna polymerase -operator (O) (LacO) that binds the lac repressor protein -the CAP binding site

Question 35

where are the regulatory regions located

Answer 35

immediately upstream of the start of transcription of the structural genes

Question 36

lac operon structural genes

Answer 36

-lacZ-encodes beta-galactosidase (cleaves lactose into glucose & galactose) -lacY- encodes a permease (helps transport lactose into the cell -LacA- encodes transacetylase (dont know function)

Question 37

how are the lac operon structural genes transcribes?

Answer 37

as a single, polycistronic mRNA, which is translated to produce the three distinct polypeptides

Question 38

where is the lacl gene?

Answer 38

next to, but not part of, the lac operon

Question 39

lacl gene

Answer 39

constitutively expressed (made all the time)

Question 40

what does lacl encode?

Answer 40

lac repressor protein

Question 41

lac repressor protein

Answer 41

-is a homo-tetramer -has a dna-binding domain that binds the the lacO sequence (operator) -has an allosteric domain that binds the inducer- allolactose

Question 42

how does the lactose operator bind to the operator?

Answer 42

reversibly -when allolactose is around, it can come off

Question 43

what does permease do

Answer 43

allows lactose into the cell, if permease gene is always off, we don't let lactose in

Question 44

how would we make allolactose if we dont have a permease?

Answer 44

we never would make allolactose

Question 45

since there is a very low basal level of transcription from the operon, what does it make this system? repressor stays on & every once in a while, it comes off randomly & the rna polymerase gets by... makes a low level basal transcription rate always

Answer 45

negative inducible control

Question 46

when lactose is + & glucose is -, what do we need to use as an energy source?

Answer 46

lactose if lactose is around, we make allolactose which binds to the allosteric domain of the lac repressor

Question 47

what does the formation of the inducer-repressor complex alter?

Answer 47

the dna-binding domain of the repressor & prevents it binding the operator -negative control (repression) is removed -transcription of lac operon is induced